This is most likely being caused by samples that the G2 is recording near the surface that are being used for the average depth calculation in Dive Log but which the G2 is ignoring. You can change the behavior of Dive Log to match that of the G2 by turning on the "Ignore Surface Samples" switch in the Dive Log Settings tab (usually under the "..." or More tab). This will change Dive Log's behavior to only consider samples deeper than 0.5 meters when calculating the average depth. This will affectedly newly downloaded dives directly, however if you want to change the result for previously downloaded dives you'll want to edit the cached "average depth" value for that dive by clearing it (tap the dive metrics and then Edit and then the "-" next to average depth). Dive Log will then dynamically calculate the average depth following the value of the "Ignore Surface Samples" switch.

If you are still finding a discrepancy after that please contact us via our support email address (support 'at' moremobilesoftware 'dot' com) and we can take some additional diagnostics steps.